Stability and Spontaneity Analyses of CO ₂ Sequestration in Cambay Shale, India: An Insight into the Sorption Thermodynamics and Pore Distribution

The sorption behavior of gases such as methane (CH4) and carbon dioxide (CO2) plays a vital role in enhancing hydrocarbon recovery from shale and advancing carbon sequestration strategies. The present study reports a detailed investigation on the sorption pattern of CH4 and CO2 on shale, utilizing high-pressure sorption, thermodynamic analyses, and low-pressure nitrogen adsorption. The pore structure distribution through low-pressure N2 adsorption identifies the dominance of mesopores with a slit type pore structure. The thermal maturity of the shale falls in the oil generation window as reported in our previous studies. The high-pressure adsorption experiment coupled with thermodynamics of adsorption, e.g., Henry’s constant, surface potential, and enthalpy of adsorption, showed high sorption capacity of CO2 over CH4 for the studied sample. The Gibbs free energy (ΔG) values for CO2 and CH4 demonstrate that CO2 adsorption is spontaneous and thermodynamically more favorable over CH4. The higher entropy change (ΔS, <0) for CO2 indicates a favorable arrangement of adsorbed CO2 with a much stable rearrangement and higher degree of molecular ordering in the adsorbed phase, with the evidence of the greater stability of CO2 on shale. Thus, the present investigation gives insight into the stability and spontaneity of CO2 adsorption and thereby its long-term storage in Cambay shale. Unlike previous Indian shale studies that primarily focused on geochemical characterization or bulk adsorption, our work integrates multiscale pore structure analyses with adsorption isotherms and molecular-level insights from the thermodynamics point of view, offering a novel perspective. Furthermore, we benchmark Cambay shale against internationally studied formations such as the Marcellus and Barnett shales (USA) and the Sichuan shale (China), highlighting similarities and contrasts in pore systems and gas sorption capacities. This comparative positioning establishes the global significance of the Cambay shale and provides a foundation for evaluating its role in both unconventional gas production and CO2 sequestration strategies.